There is a demand for effectively utilizing image content by enabling image content created under various conditions with the spread of an information communication technology to be viewed under a condition different from a condition when created. For example, in an Internet protocol television (IPTV) or the like, there are cases in which image content (a so-called network moving image) of relatively low resolution that is originally created to be viewed through a mobile terminal device or the like is displayed on an image display device of high resolution. Here, image content having resolution of 640 pixels (a horizontal direction)×360 pixels (a vertical direction) is displayed on a display that supports a full high definition (HD) standard of 1920 pixels (the horizontal direction)×1080 pixels (the vertical direction). In this case, resolution may be converted into high resolution by interpolating a signal value of each pixel included in image content between pixels (this is also referred to as up-scaling or up-conversion).
For this reason, there are cases in which the following noises are remarkably shown in an image whose resolution is increased:
(1) jaggy: a step-like contour shown in a slant line or a curved line;
(2) mosquito noise: wave-like noise shown in a portion in which a contrasting density or color signal value abruptly changes or its vicinity when a compression-coded code is decoded; and
(3) dot interference: noise shown in a granular form in a boundary in which a color changes when separation (YC separation) of a brightness signal and a color-difference signal from a composite signal is inappropriate.
In this regard, in a processing device disclosed in Patent Literature 1, a window of a certain size is set on an input current frame/field based on a current pixel, an eigenvalue and an eigenvector used to determine characteristics of the window are calculated, the characteristics of the window are determined based on the calculated eigenvalue, a filtering weighted value to be applied is decided based on the determination result, and filtering is performed on the window based on the calculated eigenvector and the decided filtering weighted value. The eigenvector includes a first eigenvector indicating a gradient direction and a second eigenvector indicating an edge direction, and the eigenvalue includes a first eigenvalue indicating dispersion in the gradient direction and a second eigenvalue indicating dispersion in the edge direction. Further, when a ratio of the first eigenvalue and the second eigenvalue is a first threshold value or less, the window is determined to be a corner region, and the filtering weighted value is set to 0, whereas the ratio is the second threshold value or larger, the window is determined to be an edge region, and the filtering weighted value is set to 1.